Mild steel is used for infrastructure applications as well as reinforcement in concrete. It is subjected to adverse environmental conditions such as weathering, ingress of chloride ions etc which causes its corrosion and results in decrease in life of the structure. Various types of organic and inorganic coating materials have been developed, however advanced coating materials with improved properties of corrosion resistance are still in demand.
Reference may be made to article “Corrosion Inhibition of Mild Steel in Near Neutral Solution by Kraft and Soda Lignins Extracted from Oil Palm Empty Fruit Bunch”, authored by Ebrahim Akbarzadefh, M. N. Mohamad Ibrahim, Afidah Abdul Rahim, International Journal of Electrochemical Science., 6 (2011) 5396-5416, wherein it is reported that soda and kraft lignin extracted from black liquor of oil palm empty fruit bunch are good inhibitors for mild steel corrosion in 3.5% NaCl at pH 6 and 8 at 25° C. The Soda lignin exhibited better inhibition compared to Kraft lignin at both pH levels and lower efficiency at a higher pH. The drawbacks of the study is that, it is based on only organic compound lignin and is devoid of other organic molecule derived species, silico-aluminous and phosphatic species which exhibit improved corrosion resistance to the substrate. Most important drawback is that, conventional coating approach to protect corrosion of mild steel was not implemented thereby preventing the studies for techno commercial application.
Reference may also be made to the article, “The role of extracted alkali lignin as corrosion inhibitor” authored by Abdel mnim Altwaiq, Sa'ib J. Khouri, Salah Al-luaibi, Robert Lehmann, Heiko Driicker, Carla Vogt, J. Mater. Environ. Sci. 2 (3) (2011) 259-270, wherein the alkali lignin extracted from sawdust of a maple wood tree was found to be good corrosion inhibitor for different alloys viz. Al—Zn alloy, stainless steel, mild steel immersed in HCl solutions. It is also reported that that the inhibition strength depends directly on the concentration of alkali lignin. The drawbacks of the coating material is that, it is based on only lignin based organic matrix and is devoid of multi element containing multi phases. Apart from this, there are no silico-aluminous and phosphatic species which exhibit improved adhesion properties and corrosion resistance to the substrate.
Reference may also be made to the article, “Corrosion Inhibition Performance of Lignin Extract of Sun Flower (Tithonia Diversifolia) on Medium Carbon Low Alloy Steel Immersed in H2SO4 Solution” authored by K K A laneme, S J Olusegun, Leonardo. Journal of Sciences, 2012, 20, 59-70 wherein, lignin extracted from sunflower was found to be an efficient corrosion inhibitor for medium carbon low alloy steel immersed in 1M H2SO4 solution. The corrosion rates were observed to decrease with increase in concentration of lignin extract but increase with temperature. The drawbacks of the study is that, it is based on only organic compound lignin and is devoid of other organic molecule derived species, silico-aluminous and phosphatic species which exhibit improved corrosion resistance to the substrate. Most important drawback is that, conventional coating approach to protect corrosion of mild steel was not implemented thereby preventing the studies for techno commercial application.
Reference may also be made to the article, “Characterization of SiO2—TiO2 Hybrid Corrosion Protective Coatings on Mild Steel” authored by Sebahattin Kirtay, Journal of Materials Engineering and Performance Volume 23(12) December 2014-4309 wherein organic-inorganic SiO2—TiO2 alcohol based ormosil solution was applied on a mild steel substrate using sol-gel based dip coating technique. The coating sols were synthesized using Glycidoxy trimethoxy silane (C9H20O5Si) and titanium tetra isopropoxide (Ti(OC3H7)4) as sources for SiO2 and TiO2 respectively. Coatings were subsequently heat treated at 200 and 300° C. to improve the corrosion resistance. The results of this work showed that specimens coated with ormosil sols possessed a higher corrosion resistance than that of uncoated specimen. The drawbacks of the coating material is that, it involves use of commercially available compounds. The developed coating material does not contain phosphate components which are well known for their corrosion inhibition properties. Apart from this, the coating process is based on sol-gel technique and involves additional heat treatment. Thus making it not suitable for commercial applications.
Reference may also be made to the article, “The Salt Spray Corrosion of Polymer Coating on Steel”, authored by Akin Akinci, The Arabian Journal for Science and Engineering 1C, 34, 139-145, 2009 wherein salt spray corrosion of polymer coating on steel substrate is reported. The process involves different pretreatments of substrate by different technique like sand blasting, chemical cleaning, and phosphating for in different time periods, followed by coating with an epoxy-polyester layer by electrostatic spray deposition method. The corrosion test was performed in 5% NaCl for over 2000 hours. The best results were obtained for substrate that were sand blasted, phosphated and coated for 3 seconds and it was also observed that polymer coating increases the corrosion resistance of steel substrate. The drawbacks of the coating material is that, commercially available epoxy-polyester compound was used as corrosion inhibitors instead of utilizing naturally occurring plants as source for organic inhibitors. The developed coating material does not contain hybrid inorganic-organic matrix and is devoid of multi element containing multi phases which exhibit improved adhesion properties and corrosion resistance to the substrate.
Reference may also be made to the article, “Potential application of geopolymers as protection coatings for marine concrete II. Microstructure and anticorrosion mechanism” authored by Zuhua Zhang, Xiao Yao, Huajun Zhu, Applied Clay Science 49 (2010) 7-12 wherein the correlations between the microstructure of the metakaolin and granulated blast furnace slag based geopolymers and their low water permeability and high anticorrosion property in sea water were investigated. Results indicated the compact microstructure of geopolymer resulting in its anticorrosion properties. The aluminosilicate geopolymerization products, unlike the hydration products of ordinary Portland Cement, were stable when immersed in sea water or exposed in air, giving marine concrete a chemical protection. It was concluded that metakaolin-based geopolymers have potential to be used as coating materials for marine concrete structures. The drawbacks of the developed coating material composition is that, it is based on inorganic matrix only and is devoid of any organic and phosphatic species which exhibit improved corrosion resistance to the substrate.
Reference may also be made to the article, “Corrosion resistance properties of hybrid organic-inorganic epoxy-amino functionalised polysiloxane based coatings on mild steel in 3.5% NaCl solution” authored by R. Suleiman, M. Mizanurrahman, N. Alfaifi, B. El Ali and R. Akid in Corrosion Engineering, Science and Technology 2013, 48 (7), 525-529 wherein hybrid organic-inorganic coatings have been developed by reacting a mixture of 3-glycidoxypropyltrimethoxysilane and tetraorthosilicat with 2-4% aminoethylaminopropyl-methylsiloxane dimethylsiloxane copolymer as a modifier. The sol-gel polymerisation of the inorganic components was achieved by base catalysation using NaOH. The resultant base coating (CGA) was further modified using two different corrosion inhibitors Molywhite 101-ED and Hfucophos Zapp. The corrosion resistant efficiency of these coatings for the protection of mild steel sheets in 3.5% NaCl electrolyte was assessed using electrochemical methods. Based on the results Molywhite based system appeared to show higher corrosion protection over that of the Hfucophos based system. The drawbacks of the coating material is that, it is based on commercially available compound rather than organic compounds extracted from naturally occurring plants as source of corrosion inhibitors. Further the developed coating material is devoid of phosphatic compounds and silico-aluminous species which provides improved adhesion properties and corrosion resistance to the substrate.
Reference may be made to patent application, “Method of Coating a Geopolymer onto an Article”, application Ser. No. 13/656,762 filed on Oct. 22, 2012, Abdullah et al, wherein geopolymer paste prepared from fly ash-derived pozzolanic material and an alkaline activator solution was coated on clay, concrete or metal with an objective to minimize surface deterioration and make them capable of withstanding severe exposure conditions such as high heat and chemical corrosion. The coated articles were cured and sintered at temperature ranging from 100° C. to 1500° C. The drawbacks of the developed coating material is that it does not contain phosphate components and organic compounds derived from natural resources which are well known for their corrosion inhibition properties and also the coating process involves sintering of coated articles at higher temperature. Thus making the whole process energy intensive.
Reference may be made to the patent application, “Geopolymer composition, coating obtainable therefrom and methods”, Application number PCT/EP 2008/002342, filing date Mar. 25, 2008, Xuhong Turella Yuanand Yuan Jinghuaet et al wherein the antirust coating was prepared by thoroughly mixing and processing filler particles, micaceous iron oxide, zinc phosphate, zinc oxide, glass scales and water in appropriate proportions. Processed material was then added to film forming geopolymer precursor consisting of aluminosilicate, alkali metal silicate and alkali metal hydroxide. The drawbacks of the developed composition prepared for coating material is that, commercially available compounds were used instead of utilizing naturally occurring plants as source for preparation of anti rust coatings.
Reference may be made to the patent application “Geopolymer precursor dry mixture, package, processes and methods”, application number U.S. Ser. No. 12/952,239, filing date Nov. 23, 2010 Chan Han et al wherein geopolymer precursor consisting of dry mixture of metal silicate powder, aluminosilicate powder and alkali. Other supplemental organic and inorganic ingredients were also added to the dry precursor for improving its performance. The developed composition was used for coating applications to variety of substrates such as metal, wood, polymer, ceramics etc. The drawbacks of the developed composition prepared for coating material is that, the geopolymer precursor dry mixture was merely a physical mixture of various constituents and no solid state chemistry was involved, large number of commercially available compounds were used for preparation of coating material, apart from this, no phosphatic compounds were added which provides improved adhesion to the metal substrate and additionally provide corrosion inhibiting properties.
From the above mentioned prior art and based on the drawbacks of the conventional processes, the various issues to be addressed and problems to be solved are as follows:
a) The work so far carried out in the area of development of geopolymeric coating materials is basically restricted and is essentially based on solution chemistry.
b) Absence of together mechanico-chemical dry grinding of raw materials and synergistic and simultaneous solid state reactions among them in conventional geopolymeric system prohibits in tailoring of the developed material for desirable properties.
c) Already existing coating material contains inorganic matrix only. Lack of simultaneous presence of inorganic-organic molecules resulting in development of non homogeneous matrix, poor adhesion and corrosion resistance properties.
To over come these drawbacks, the nano phosphatic hybrid inorganic-organic, multi elemental and multi phases containing geopolymeric corrosion resistant coating material is developed in the present invention. It will be an advancement which will significantly contribute to increase the life of infrastructure based on mild steel by preventing deterioration of their surface due to corrosion.